I was fortunate enough to receive a response from Tobi Oetiker clearing up some of my misconceptions about RRD ie. you can read the response here
http://vuksan.com/blog/2010/12/14/misconceptions-about-rrd-storage/#comment-7728 When you update an rrd file only the data which changed is written to the rrd file (hence the circular buffers) ... due to the way hard diskts work, a whole block has to be written for every write (which is ~4096 bytes) it is still much less than the whole file ... run rrdtool with strace to see for yourself. When using rrdcached, it will collect multiple updates before writing them to disk. Theoretically you could see a performance improvement by a factor of 512 since it would only write a single block 8 * 512 bytes for 512 updates of one 8 Byte number. Based on this input I propose we change the default storage options for Gmetad. Currently settings are as follows in gmetad/conf.c.in config->num_RRAs = 5; config->RRAs[0] = "RRA:AVERAGE:0.5:1:244"; config->RRAs[1] = "RRA:AVERAGE:0.5:24:244"; config->RRAs[2] = "RRA:AVERAGE:0.5:168:244"; config->RRAs[3] = "RRA:AVERAGE:0.5:672:244"; config->RRAs[4] = "RRA:AVERAGE:0.5:5760:374"; I propose we change it to have full resolution for up to two weeks ie. 244*24*14 = 81984 and have averages for 2 years ie. config->num_RRAs = 3; config->RRAs[0] = "RRA:AVERAGE:0.5:1:81984"; config->RRAs[3] = "RRA:AVERAGE:0.5:672:244"; config->RRAs[4] = "RRA:AVERAGE:0.5:5760:748"; You can still override the settings in gmetad.conf but we should start with higher defaults. Does this sound reasonable ? Vladimir ------------------------------------------------------------------------------ Lotusphere 2011 Register now for Lotusphere 2011 and learn how to connect the dots, take your collaborative environment to the next level, and enter the era of Social Business. http://p.sf.net/sfu/lotusphere-d2d _______________________________________________ Ganglia-developers mailing list Ganglia-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/ganglia-developers
